The use in optical technology of a Fresnel lens to obtain a general collimation effect with a reduced lens thickness is known.
A lens of this type is, for example, disclosed in the patent application published as JP 2002-221 605. This lens collimates the incident ray sent by a light source. To do this, the lens comprises prismatic elements that rectify the rays received from the source into a beam of parallel rays.
This lens is, for example, used in a projection display device. In practice, in such a device, a small imager is project onto a display screen by a projection system, with angles of incidence on the screen that extend over a determined range of values, for example from 30° to 60°.
The flow received from the projection system must therefore be globally collimated by a Fresnel lens, that is, rectified in a horizontal direction, before being generally micro-focused through a dark matrix then diffused in the desired observation field.
According to JP 2002-221 605, the design of the lens is such that the prismatic elements which receive the rays with a low angle of incidence work in refraction mode whereas those that receive rays with a high angle of incidence work in reflection mode.
The result is good efficiency in the region of the high angles of incidence and in the region of the low angles of incidence. In the intermediate region, however, the efficiency remains mediocre regardless of the type of prism used.